1. Field of the Invention
The present invention relates to navigational devices. More particularly, the invention relates to a combined GPS receiver and depth sounder unit that includes a single display screen that can be smoothly adjusted so that the area of the display screen devoted to a GPS map can be changed relative to the area devoted to a depth sounder display.
2. Description of the Prior Art
Many types of navigational devices exist for both recreational and professional use. For example, many fishermen, boaters, and other sportsmen use GPS receivers to determine and view their current location and depth sounders to determine the depth of a body of water.
Recently, GPS receivers and depth sounders have been combined in single units to permit users to determine both their current location and the depth of a body of water. These combined units typically include a single display screen that displays both a GPS map display and a depth sounder display.
Combined GPS receivers and depth sounder units allocate a fixed amount of their display screens for the GPS map display and the depth sounder display, for example, approximately 75% for the GPS map and approximately 25% for the depth sounder display. This fixed division of the display screen is a limitation because users may wish to adjust the relative size of the GPS map and depth sounder displays in certain circumstances. For example, a fisherman who is primarily interested in determining and viewing the depth of a body of water may wish to enlarge the depth sounder display relative to the GPS map display to provide more resolution for the depth display.